Effect of crystallinity on the frictional and wear performance of molybdenum disulfide: A molecular dynamics study

Abstract: The frictional and wear performance of molybdenum disulfide (MoS2) is significantly influenced by its intrinsic arrangement of crystals or crystallinity. In this study, we investigate the effect of crystallinty on coefficient of friction (COF) and wear in MoS2 using a suite of reactive molecular dynamics (MD) simulations. A range of configurations, from amorphous to crystalline, is modeled to capture the effect of structural order on the tribological behavior. To study friction and wear, we simulate the sliding of a spherical rigid carbon body over the MoS2 surface under varying crystallinity conditions. Our results reveal a pronounced reduction in COF with decreasing crystallinity, with crystalline MoS2 exhibiting superlubricity. This behavior is attributed to the preservation of a flat sliding surface and frictional anisotropy, which enables lateral movement along low-resistance paths. In contrast, amorphous and polycrystalline MoS2 with lower degrees of crystallinity displays a substantially higher COF, driven by increased surface roughness and atomic-scale energy dissipation. Furthermore, we examine the wear mechanisms under high normal loads, demonstrating that crystallinity enhances wear resistance by mitigating material deformation. These findings provide atomic-scale insights into the tribological performance of MoS2, emphasizing the critical role of structural order in achieving ultralow friction. Our work corroborates with previous studies on superlubricity in MoS2 and extends this understanding to rigid-body sliding conditions, offering valuable implications for designing low-friction and wear resistant solid lubricants.